Benzo(a)pyrene (B[a]P) is a typical kind of polycyclic aromatic hydrocarbons (PAHs) often found in soils adjacent to the oil field or in soils irrigated with sewage. Collembolans are often used as sensitive receptors in ecological risk assessment of contaminated soils and in development of soil ecological benchmarks. However, the characteristic indices, such as growth rate, fatality and reproduction rate of their adults, were only responsive to high concentrations of B[a]P in the soil. In the present study, Folsomia candida was used as subject for ecotoxicity test to screen out new characteristic indices sensitive to low concentrations of the substances Besides, comparison was made between two typical zonal soils, i.e. udic-ferrosols and aquic-cambosols in sensitivity of the subject insects. Results show that the index of growth rate of their larva was the most sensitive and even responsive to a low concentration of B[a]P. It is, therefore, suggested that the index be cited as an indicator of the soil B[a]P toxicity. The four indices followed an order of juvenile length > adult length > reproduction rate > survival rate in sensitivity. Significant difference in ecotoxicity of B[a]P to F. candida existed between the two soils with LOEC value being 1 mg kg^-1 in udic-ferrosols and 100 mg kg^-1 in aquic-cambosols, which is likely attributed to the difference in soil physico-chemical property, especially content of organic matter and pH. It is, therefore, necessary to normalize ecotoxicity data of various soils in developing soil ecological benchmarks.